Virtually every full-time or part-time four-wheel drive consumer vehicle, i.e., passenger car, truck or sport utility vehicle utilizes a transfer case to direct a portion of the drive torque to a secondary driveline and drive wheels. Given the increased popularity of trucks and four-wheel drive vehicles, significant and increasing attention has been directed to the mechanical configuration of transfer cases.
One of the areas of development relates to the torque throughput of the transfer case and the myriad competing parameters which affect it. Torque throughput parameters involve issues such as size of the transfer case, size of the clutch, power consumption of the clutch, duty cycle of the clutch, power transfer demands of the vehicle, desired efficiency and many other physical and functional considerations.
One of the most obvious approaches to increasing the torque throughput capability of a transfer case clutch is the apparently simple expedient of increasing the size of the clutch. However, this expedient increases the size of the transfer case and its weight, two changes that are highly inimical to vehicle weight reduction and control programs. Secondly, a larger clutch will generally require greater electric or hydraulic power to effect its operation. This, too, is counterproductive to overall vehicle efficiency.
Accordingly, clutch configurations that do not involve either significant enlargement of components or increase the number of components in a transfer case are looked upon with great favor.